User blog comment:FluffyMermaid78/All of Pokémon could end soon... (theory)/@comment-32077647-20180523153950

From I Choose you movie, they were gym leaders so they cannot travel with ash so they would replaced them with new characters, but in there real series, they traveled with ash but in the movie,they had gym battles to finish.

Misty and Brock aren't dead, if they were.. then who would take care of the cascade gym or boulder gym? (Name badge)

They were replaced by new characters only to take care of their gyms.

For sun and moon, it was only a vacation but when mr. mime won a raffle, they went to Alola for a vacation but ash found pokemon school, gyms and leagues aren't available for a small island